我們以自製的磁光柯爾效應儀 (SMOKE) 探測Ag超薄膜覆蓋於Co/Pt(111)樣品前後之表面磁性變化,並藉由歐傑電子能譜術 (AES) 鑑別樣品表面組成成分、計算薄膜厚度,以及低能量繞射電子儀 (LEED) 研究表面結構,升降溫系統與離子濺射進行退火效應與深度分析的實驗。
我們發現在1ML及2ML Co/Pt(111)其樣品磁化易軸在垂直樣品表面方向,近1ML的Ag覆蓋會增強矯頑力HC達到最大的幅度。而1ML Ag/1ML Co/Pt (111)經650K退火後,因Co-Pt合金的形成,室溫下polar方向的柯爾訊號增至退火前200%,但經710K退火的樣品則因室溫325K時HC大於外加磁場而量測不到柯爾訊號。至於1ML Ag/2.2ML Co/Pt (111)磁性變化則與1ML Ag/1ML Co/Pt(111)相類似,但因Co厚度增加使得居禮溫度由後者之710K提高至780K,此外室溫325時之HC尚小於外加磁場,故可量測到柯爾訊號。
3ML Co/Pt(111)則因Co薄膜呈三維島狀成長,使樣品磁化易軸提前轉為平行樣品表面的方向,但經1ML的Ag覆蓋後,產生spin reorientation transition (SRT)的現象,磁化易軸轉為垂直樣品表面的方向;同樣的現象在4ML Co/Pt(111)及5ML Co/Pt(111)中發現,並經由深度分析確定SRT的產生機制來自Ag覆蓋層的影響。同時我們也觀察Ag覆蓋後樣品升降溫過程的磁性變化,並在論文討論之。
而8ML Co/Pt(111)則在Ag覆蓋厚度達1.5ML層時,才量測到polar方向的柯爾訊號,我們推測Ag覆蓋層達1ML時已增強垂直磁異向性,只是HC大於外加磁場而量測不到訊號,隨著Ag覆蓋層厚度增加HC減小而測得柯爾訊號。此外我們並不確定是Ag-Co介面或者是量子效應干涉造成這樣的現象,值得再深入研究。
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